H. S. Stannus 
361 
the melanoblasts of one and the other are independent structures. The nature of 
melanin has been investigated by a few observers. Hopkins and Cole have isolated 
a substance as a product of tryptic digestion of proteid which may be the mother 
substance of the proteinochromes skatol, pyridine and tyrosine. Tyrosine by the 
action of a ferment can be changed into a substance resembling melanin. 
This ferment tyrosinase has lately been found in a variety of species, plants 
and animals, including newborn rabbits, rats and guinea-pigs. 
The above notes on melanin are gleaned from Pearson's observations on 
Von Furth's summary. 
Dyson has recently shown, by means of the bichromate-haematoxylin method 
of Lorrain Smith and Mair, that pigment is always formed as part of a complex 
granule which contains lipoid substance. These granules are present constantly 
in the basal epithelial cells, and are formed there under the influence of the 
nucleus as a part of the normal metabolism of the cell. The pigment is in origin 
a lipochrome, the melanin being the chromatic proteid portion after separation 
from the complex lipoid granule. He found no evidence of pigment formation in 
the cutis, but showed sections which illustrated the passage of lipoid substances 
from the epidermis into the cutis along lymphatic channels. 
It appears therefore that our knowledge on melanin and its pixxluction so far 
points to the following conclusions : 
(1) Melanin is not a direct (and probably not an indirect) product of 
haemoglobin. 
(2) It is the product of splitting of a complex lipoid substance possibly as 
the result of a ferment action, akin to the formation of pigment from tyrosin by 
tyrosinase. 
(3) The complex granules containing the lipoid substance are produced as 
the result of the metabolic activity of the individual cells of the epiderm. 
(4) The presence of melanin is responsible for skin pigmentation. 
(5) Melanin in the cutis is probably derived from the epidermis. 
This is as far as knowledge goes at present with regard to melanin. How can 
we explain its more or less complete absence in albinism, etc. ? Pearson sums up 
" when we consider the relative rareness of conrplete albinism, of the spotted or 
splashed condition and of Xanthism, their relatively frequent coincidence in the 
same stock suggests that these abnormal pigment conditions are not wholly 
independent, and that as a working hypothesis it is reasonable to suppose that 
complete albinism, partial albinism, incomplete albinism and Xanthism, all static 
forms of leucosis, are phases of the same process and are probably linked with 
leucoderma and possibly other forms of dynamic leucosis. By ' linked ' we suggest 
that they mark the complete, incomplete, local or progressive failure of the same 
metabolic process, which may never start at all, never start in certain areas, or be 
imperfectly started, and again being started may fail to maintain itself ; further 
